In the Theme task pane, right-click the thumbnail for the theme you want to edit, and then click Edit.
Note: If you don’t see the Theme task pane, on the Format menu, click Theme.
In the Edit Theme Colors or Edit Theme Effects dialog box, choose the options you want, and click OK.
Note: You can’t edit the built-in themes that are included with Visio. If you want to make a change to one of the built-in themes, duplicate it and then edit the duplicate theme.